Select the option that best completes the sentence.The mass of the neutron is approximately equal to the mass of the: protonelectronnucleus

To determine which option best completes the sentence "The mass of the neutron is approximately equal to the mass of the:", we need to consider the masses of subatomic particles.

1. Mass of a Proton: The mass of a proton is approximately $1.67 \times 10^{-27}$ kg.
2. Mass of a Neutron: The mass of a neutron is about $1.68 \times 10^{-27}$ kg.
3. Mass of an Electron: The mass of an electron is significantly smaller, approximately $9.11 \times 10^{-31}$ kg, which is about 1/1836 the mass of a proton.
4. Mass of the Nucleus: The nucleus consists of protons and neutrons; thus, its mass will vary depending on the number of those particles it contains, but it will not be an exact equivalent.

Analysis

• When comparing the mass of the neutron specifically to the mass of these particles:
  • The neutron and proton masses are very close.
  • The electron mass is negligible in comparison.
  • The nucleus's mass cannot be directly equated to a single particle like a neutron.

Conclusion

Given that the neutron's mass is approximately equal in size to that of a proton, the best option to complete the sentence is:

The mass of the neutron is approximately equal to the mass of the proton.